yocto/fvp-rd-n2-automotive: Update model recipe for release candidate

Now that an 11.20.x release candidate is available, replace
BB_STRICT_CHECKSUM with the sha256 of the release candidate tarball.

The license agreement has changed in the release branch, so update
LIC_FILES_CHECKSUM.

Issue-Id: SCM-5314
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: I52d84971ca21e7b9a698e4902b3ddc3e51050590